The present invention relates to an apparatus for achieving liquid-liquid extraction of the mixing/settling type used to prepare samples intended for checking the quality of any type of water, e.g., sea water, ground water, surface water and, more particularly, water treated in a water treatment plant.
Checking the water quality requires analysis made continuously on samples transmitted to a laboratory from their sampling site. To carry out these analysis, samples are taken of the constituents to be metered, such as organic compounds (e.g. pesticides) polycyclic or aromatic hydrocarbons, etc., so as to concentrate them to facilitate further analysis.
The extraction of the organic compounds to be proportioned is carried out in the known manner by means of a suitable organic solvent in specific operating conditions obtained by the addition of reagents.
This liquid-liquid extraction usually is carried out by means of laboratory equipment, e.g., extraction flasks agitated by mechanical means. These devices require large volumes of solvent and limited volumes of water samples. They further have the disadvantage that they work discontinuously and require constant supervision.
More complex, continuously operating devices have already been described that admit of a liquid-liquid extraction in a laboratory. This type of apparatus is classified into several categories. In some of them, the mixing takes place in containers under continuous agitation in order to increase the liquid-liquid interface.
Also, there is a laboratory apparatus in which the liquid-liquid contact is assured by the passage of the liquids in a helical coil made of teflon. The water that is to be analyzed and the solvent are mixed prior to entry into the coil. This coil is placed horizontally and the mixture is introduced according to a pulsed flow.
According to a third type of prior art apparatus, the water to be extracted and the extraction solvent are introduced into a column. Since this apparatus is provided for the use of solvents that are lighter than water, the latter is introduced at the top of the column, while the solvent is introduced at the bottom. The water, freed from the products that are soluble in the solvent, is collected at the bottom, the solvent charged with these products appearing at the top and being subjected to distillation prior to being recycled in the extraction process.
This type of prior art apparatus has several disadvantages to the extent that its use is limited to laboratories. In order for this apparatus to be suitable for use in places where the water to be analyzed is located, it must be able to withstand transportation, that is to say, it must include only leak-proof containers of robust construction and must not be of complex construction so as to reduce the risk of breakdown.
Since usually the product to be extracted has a weak concentration, a continuous operation is highly preferred in order to be able to treat considerable quantities of water.
Likewise, because of the weak concentrations of the products that are to be analyzed, it is desirable that they be extracted on site, if possible. In fact, the taking of samples, their transmission and storage provide many occasions for introducing into the samples other or the same contaminants, which distort the analysis.
Another drawback of the prior art equipment is the treatment of the solvent. As a rule, the solvent is recycled in the extraction process after it has been distilled at the boiling temperature. However, during distillation impurities can be carried along, which also leads to false results.